WO 2011/120113 [U.S. Pat. No. 8,442,775] describes a system and a method for monitoring gases in power transformers cooled by oil. In that case, the system consists of a rod and a main housing. The rod has two conduits running in the interior and is positioned in the oil of the power transformer. The conduits are connected together by two oil chambers and a pump so that the oil is sucked from the power transformer via a conduit to the first oil chamber and can be subsequently introduced by the second oil chamber through the other conduit back into the power transformer. The pump is in that case provided in a conduit section between the oil chambers. An additional region with a temperature detector and a moisture sensor is present in front of the pump. The two oil chambers have a wall consisting of a semipermeable material. Gases present in the oil of the power transformer can migrate through this wall into the interior of the main housing. An additional gas sensor detects the gases that collect in the main housing of the system. In addition, two valves each with a respective filter are provided at the housing. One of the valves is used for sucking air from the environment by a pump. The air is expelled from the interior of the main housing through the second valve. The system is controlled by a control.
This known system is of very complicated construction. The multiplicity of individual parts used means that the system is not only expensive, but also maintenance-intensive. The valves for the air exchange wear particularly quickly and thus form a weak point in the system. The flatly constructed membrane can rupture particularly quickly in the case of a sudden pressure rise and especially at the time of evaluation of the carrier gas.
U.S. Pat. No. 6,526,805 describes an apparatus for continuous analysis and measurement of the content of gas components in an insulating liquid substantially on a real-time basis. This apparatus comprises a gas extraction unit for separation of the gases from the liquid, an infrared gas analyzer for determining the concentration of the individual gas components, a gas pump for circulating the gases to the gas extraction unit in a closed loop and a calibrating device for the infrared gas analyzer. The gas extraction unit comprises a gas-permeable polymer membrane and a gas chamber with a gas flow inlet and a gas flow outlet. The infrared gas analyzer comprises an infrared source, a gas cell with a gas inlet and gas outlet and a quad-detector with extremely narrow-band optical infrared filters. The calibrating device comprises a valve device for flushing out the gas components with air and for resetting the infrared source to zero. The valve device comprises a first three-way valve that is seated between the gas pump and the gas extraction unit, and a second three-way valve that is seated between the gas cell and the gas pump.
U.S. Pat. No. 8,075,675 describes an apparatus for extraction of gas from a liquid. This apparatus comprises a housing, a separating membrane in the housing, a porous membrane support, an oil pump, a gas pump, a gas distributor and an analyzing instrument. The housing defines a fluid path and a gas path that is isolated from the fluid path, and has an inlet to the fluid path, an outlet from the fluid path, an inlet to the gas path and an outlet from the gas path. The separating membrane separates the fluid path from the gas path and comprises a fluorosilicone element that is impermeable to the liquid and permeable to the gas. The separating membrane has a first side facing the fluid path and a second side facing the gas path. The separating membrane forms a flattened disk that is thicker at the edge and thinner in the center. The membrane support faces toward the first side of the separating membrane. The fluid path contains the first side of the separating membrane. The oil pump conveys the liquid through the fluid path. The gas pump conveys a carrier gas and the gas that is released from the liquid, through the gas path. The analyzing instrument is connected with the gas path by the gas distributer. The gas distributor is described in detail in U.S. Pat. No. 6,391,096 and comprises seven control valves.